During the day, (Lights ON) the plant is collecting and storing light energy, and is using and storing raw materials. The plant is stockpiling raw material, and is charging its batteries
it is ALSO using raw materials and using the energy it is collecting. Its building itself, literally putting itself together.
During the day however, the plant is not as efficient at building itself, as it is at night (lights OFF.) It can build itself, but not as quickly.
While the lights are OFF, the plant is using energy and raw materials to build itself
. the plant is more efficiently using the raw materials that it stored during the day. The plant is better at transporting and assembling the raw materials.
...
Although the plant IS capable of doing it all with the lights on, (Collect, store and use energy & raw materials) it does a better job of actually doing the work (using the energy and raw material) while the lights are out. During the dark however, it relies solely on its limited supply of stored energy and stored raw material.
One last thing to remember is the fact that a plant will always strive to maintain a balance between the size of its roots and the size of its canopy (Leaf mass.) The roots must be big enough to supply as much raw materials as the canopy can use, and the canopy must be big enough to provide the energy required to store those raw materials
.
...
If the plant is already in balance, the canopy and the roots will grow at the same rate.
If you actually measured them several times daily over several days, youd notice that they actually DO get bigger at night, but roots and canopy at the same rate, unless either has been trimmed, and as long as the batteries hold out.